1. Field of the Invention
The present invention relates to a communication system that transmits a plurality of pulse signals, a transmission circuit and a reception circuit included in the communication system, and an image forming apparatus including the communication system.
2. Description of the Related Art
An image forming apparatus uses, for example, a plurality of pulse motors having excellent positional control properties to convey papers. The speed of pulse motors is indicated by a pulse width. In recent years, control therefor has become complicated and the circuit size of a pulse signal generator has become large.
In view of the above, Japanese Patent Laid-Open No. 2000-324896 discloses a configuration shown in FIG. 9 where the circuit size is restrained by providing a pulse signal generator in a controller that centrally controls the apparatus, instead of providing pulse signal generators in correspondence with drivers for pulse motors. Japanese Patent Laid-Open No. 2000-324896 further discloses a configuration where the transmitting end executes parallel-serial (PS) conversion for time-division multiplexing on a plurality of pulse signals to reduce communication lines for transmitting the pulse signals to the drivers. In this case, as shown in FIG. 9, the receiving end obtains the pulse signals for the drivers by executing serial-parallel (SP) conversion.
However, in the case where sampling and time-division multiplexing are executed on the pulse signals, the pulse widths of the pulse signals restored by the receiving end may differ from the pulse widths of the pulse signals at the transmitting end. This phenomenon is described below with reference to FIG. 10. Referring to FIG. 10, the high level and the low level of the transmitted pulse signal both last for five unit times, and PS conversion is executed on the transmitted pulse signal while sampling the transmitted pulse signal at a sampling interval of three unit times. Note that the solid arrows shown in FIG. 10 indicate sampling timings. Meanwhile, the receiving end restores the received pulse signal using the sampled values, and therefore the pulse width of the received pulse signal differs from the pulse width of the transmitted pulse signal as shown in FIG. 10.
In a signal whose pulse width represents a control parameter, fluctuations in the pulse width mean occurrence of control errors. For example, in the case of control for the aforementioned pulse motors, fluctuations in the pulse widths lead to errors in the speed of conveyance of papers, and such errors may give rise to asynchronism depending on properties of the pulse motors. Although it is possible to shorten a sampling period to suppress fluctuations in the pulse widths, doing so increases the speed of the multiplexed signal and therefore requires measures against noise such as shielding of communication lines or differential transmissions, thus leading to a significant cost increase.